1. Field of the Invention
The present invention relates generally to the field of asphalt compositions and various methods for the preparation of these compositions. More particularly, the present invention relates to asphalt compositions whose preparation includes the addition, at specific times, of both a polymer and a source of polyphosphoric acid. The present invention thus relates to an asphalt composition of the type that can be termed polymer modified.
2. Discussion of the Related Art
Historically, polymers have been added to asphalt compositions. Prior art polymer asphalts of the type hereunder consideration, sometimes called polymer modified asphalts, are well-known to those skilled in the art. A conventional polymer modified asphalt is typically based on the addition of thermoplastic elastomer to the asphalt. The polymer improves the performance of the asphalt. However, polymer additives are relatively expensive. Thus, a previously recognized problem has been that polymer modified asphalts are costly.
In the past, mineral acids have been added to asphalt compositions. Prior art acid containing asphalts of the type hereunder consideration, sometimes called acid modified asphalts, are also well-known to those skilled in the art. A conventional acid modified asphalt is typically based on the addition of a mineral acid to an air blown asphalt. For example, polyphosphoric acid (i.e., H.sub.n+2 P.sub.n O.sub.3n+1, where n&gt;1) can be added to air blown asphalt in the form of phosphorus pentoxide (i.e., P.sub.2 O.sub.5). The acid improves the low temperature performance of the air blown asphalt. A previously recognized problem has been that adding polyphosphoric acid to air-blown asphalt yields a trade-off between properties.
Oil refineries are designed to refine specific types of crude oils. A refinery designed to refine light sweet crude would not be able to efficiently refine a heavy crude, if at all. The heavy crudes do not require as severe processing as do the light crudes.
Sweet and sour crudes are so defined based on the percentage of sulfur contained in the crude. The breaking point between sweet and sour crudes is not well defined, but generally less than 2 weight percent is considered to be sweet, while greater than 2 weight percent is considered to be sour. The majority of the sulfur in the crude remains in the highest boiling point fraction or the bottom residuum, the asphalt. Since a light sweet crude might yield only 15% asphalt, and a heavy sour crude might yield 50% asphalt, the asphalt from the light sweet crude may actually contain a larger percentage of sulfur.
Heavy and light crudes are so defined based on the API gravity or specific gravity of the crude. The API gravity and specific gravity are related by the following equation, S.G.=(141.5)/(131.5+API) where the higher the API, the lower the S.G. High API gravities are indicative of light crudes, while low API gravities are indicative of heavy crudes. The breaking point between heavy and light crudes is not well defined, but generally an API gravity less than 25 is considered to be heavy, while an API gravity greater than 25 is considered to be light.
An aromatic compound is described as those compounds having physical and chemical properties resembling those of benzene. A naphthenic compound is described as those compounds having physical and chemical properties resembling those of cyclopentane, cyclohexane, cycloheptane, or other naphthenic homologs derived from petroleum. Generally, the breaking point between aromatic and naphthenic asphalts is considered to be 70% cyclics from an Iatroscan analysis. Greater than 70% cyclics is considered to be aromatic, while less than 60% is considered to be naphthenic.
The Strategic Highway Research Program (SHRP) was established in 1987 to improve the performance and durability of United States roads and to make those roads safer for both motorists and highway workers. One of the results of SHRP was the development of the Superior Performing Asphalt Pavements (SUPERPAVE.TM.) specifications for asphalts. The SUPERPAVE.TM. system specifies materials characterization techniques and results thereof for the performance certification of asphalt within temperature ranges (e.g., 70-22:from +70.degree. C. to -22.degree. C.). By specifying the acceptable limits for the characterization results, rather than any particular composition, the SUPERPAVE.TM. specifications are material independent. Thus, an end user can require that an asphalt meet a particular SUPERPAVE.TM. specification and be reasonably confident that an installed asphalt will perform satisfactorily, without regard to the specific crude oil source or other compositional parameters, thereby controlling rutting, low temperature cracking and fatigue cracking. Thus, a recently recognized need has developed for compositions and methods that meet the SUPERPAVE.TM. specifications consistently and efficiently.